Combustion engines are often used for power generation applications. These engines can be gaseous-fuel driven and implement lean burn, during which air/fuel ratios are higher than in conventional engines. For example, these gas engines can admit about 75% more air than is theoretically needed for stoichiometric combustion. Lean-burn engines increase fuel efficiency because they utilize homogeneous mixing to burn less fuel than a conventional engine and produce the same power output.
Though using lean burn may increase efficiency, gaseous fuel-powered engines may be limited by variations in combustion pressures between cylinders of the engine. Gaseous fuel-powered engines are typically pre-mix charge engines, where fuel and air are mixed within an intake manifold and then admitted to a combustion chamber of the engine. Variations in combustion pressure result from more air/fuel mixture being admitted into some cylinders than into other cylinders. This uneven distribution of the air/fuel mixture can result in pockets of the air/fuel mixture burning outside of the envelope of normal combustion, increasing the tendency for an engine to knock. The combustion pressure variations can result in cylinder pressures that are significantly higher than average peak cylinder pressures normally seen within the engine. And, because significantly higher cylinder pressures can cause the engine to operate improperly, a margin of error is required to accommodate the pressure variations. As a result, the engine may be required to operate at a level far enough below its load limit to compensate for the pressure variation between the cylinders, thereby lowering the load rating of the engine. Additionally, the pressure variations can cause fluctuation in engine torque and speed, which may be undesirable for some electrical power generation applications.
One attempt to reduce pressure variations within an engine is described in U.S. Pat. No. 5,027,769 (the '769 patent), issued to Yoshida et al. The '769 patent discloses an engine system having an air intake. The intake includes multiple intake passages, each intake passage including a throttle valve. The '769 patent also discloses a control apparatus and a sensing device for detecting abnormalities in throttle valve operation. The control apparatus adjusts the operation of the throttle valves based on input from the sensing device, thereby adjusting an amount of air/fuel mixture delivered to the engine. By this adjustment, an appropriate amount of air/fuel mixture may be delivered to the engine, thereby maintaining a desired combustion pressure despite the occurrence of abnormalities in one of the multiple intake passages.
Although the control apparatus of the '769 patent may control a plurality of throttle valves based on sensed data relating to abnormal operation, the apparatus may incur a lag time between adjustment of the throttle valves and a corresponding change in the amount of the air/fuel mixture delivered to the cylinders. The lag time may occur because it takes an amount of time such as, for example, about 3-5 seconds between adjusting a throttle valve and a corresponding change in combustion pressure to occur within the cylinders. The lag time may reduce the responsiveness of the engine to engine speed adjustments, which may be undesirable for operation.
The present disclosure is directed to overcoming one or more of the shortcomings set forth above and/or other deficiencies in existing technology.